Weight

[Hurry- Starfish!]

I just use whatever parts seem suitable as a dummy payload.

The reactors from Near Future Propulsion are quite heavy for example, so I used a few of those the last time I designed an SSTO.

...Stresstesting an experimental spaceplane by loading it with nuclear reactors might not be the safest thing to do. But it's quite kerbal!

[bonyetty]

Test? There is no test. Just do. Just explode. Just not quite make orbit. Just have way too much delta V. Just have fun. I just do that.

[SRV Ron]

I use the Kerbal School of Hard Knocks method. I start with a payload and build around it until it gets into orbit. Then, I refine the design for better efficiency.

[NecroBones]

So how do you test weight capabilities of your rockets? Do you use dummy payloads or mods?

I didn't originally. For a long time, I just built something specific to the payload, eyeballing it, until it looked good enough to do a test. If it didn't make orbit, I added more boosters or something, and tried again. Trial and error, with usually only a couple of test launches needed, if that. Sometimes it was just fine as is.

With ARM, I decided to standardize my lifters, so I made test payloads with precise weights, at 50, 75, 100, 125, 150, and 200 tons. I tuned lifters to handle the 50, 100, 150, and 200 ton weights such that they could get the payload into a 150km circular equatorial orbit, with the last stage of the lifter attached with about 25% or 33% of its fuel left (for a margin of error in payload weights, or launching into more inclined orbits). Since then I've also added a 275 ton category (because one of my asteroid tugs hit that weight).